Effect of oenological practices on microbial populations using culture-independent techniques

Sulphur dioxide (SO2) addition and yeast inoculation are well-established practices in winemaking for restricting the growth of indigenous yeasts and bacterial populations. The effect of these oenological practices on wine microbial populations has been evaluated using culture-independent methods. These are quantitative PCR (qPCR) for the enumeration of yeasts, lactic acid bacteria (LAB) and acetic acid bacteria (AAB), and PCR-DGGE to determine the yeast and bacteria species diversity. The PCR-DGGE method detected a low yeast and bacteria species diversity. On the contrary, the specificity of the primers designed for the qPCR allowed that minor microbial groups such as Hanseniaspora were accurately quantified regardless of a large presence of other microbial groups such as Saccharomyces. From an oenological point of view, inoculation increased the proportion of Saccharomyces vs. non-Saccharomyces in a shorter time. Hanseniaspora increased during the first phase and decreased during the latter phases of the process, especially in the sulphited fermentations. Both yeast inoculation and SO2 kept the LAB populations at very low level, while the AAB populations were hardly affected by these two practices.